There are a number of different ways to assemble a rotary structure, such as a dynamoelectric machine rotor. For example, in a single or double insulated motor, it may be necessary to place an electrically insulative member between a rotor shaft and a rotary body mounted thereon comprising a stack of laminations. FIGS. 6A and 6B illustrate a prior art fiberglass sleeve 2 having an inner surface 4 and an outer surface 6. The fiberglass sleeve 2 has been utilized having an outer diameter which is slightly less than an inner diameter of a bore extending through the stack. After the sleeve 2 is placed in a bore, a metal rotor shaft having an outer diameter slightly greater than the inner diameter of the fiberglass sleeve 2 is forced into the fiberglass sleeve 2, causing the fiberglass sleeve 2 to expand radially outwardly into contact with the walls defining the bore. The dimensions of the various parts are selected such that the laminations are trapped on the outside of the sleeve 2 and thereby fixed in position.
While the foregoing assembly has been effective to securely assemble the various parts together, it has been found that relatively high assembly pressures must be utilized to insert the metal shaft into the fiberglass sleeve 2. These assembly pressures can cause the shaft to bend or flare out undesirably on the end that is pressed.